Those who have irregular blood glucose concentration levels are medically required to regularly self-monitor their blood glucose concentration level. An irregular blood glucose level can be brought on by a variety of reasons including an illness such as diabetes. An estimated 18 million people are afflicted with diabetes in the United States alone. A diabetic patient typically monitors his or her blood glucose concentration level to determine whether the level is too high or too low, and whether any corrective action, such as administering insulin or other medication, is necessary to bring the level back within a normal range. The failure to take corrective action can have serious implications. When blood glucose levels drop too low—a condition known as hypoglycemia—a person may become nervous, shaky, confused, have an impaired judgment, and eventually pass out. A person can also become very ill if their blood glucose level becomes too high—a condition known as hyperglycemia. Both hypoglycemia and hyperglycemia can potentially be life-threatening emergencies. As a result, a diabetic may require frequent sampling of his or her blood glucose—typically several times per day.
In one type of blood glucose testing system, sensors are used to test a sample of blood. Such a sensor may contain bio-sensing or reagent material that will react with blood glucose. The testing end of the sensor is adapted to be placed into the fluid being tested, for example, blood that has accumulated on a person's finger after the finger has been pricked. In one type of sensor, for example in U.S. Pat. No. 5,100,620, issued Mar. 31, 1992, and entitled Capillary Tube/Gap Reagent Format, the fluid is drawn into a capillary channel that extends in the sensor from the testing end to the reagent material by capillary action so that a sufficient amount of fluid to be tested is drawn into the sensor. For electrochemical sensors, the fluid then chemically reacts with the reagent material in the sensor. The chemical reaction results in an electrical signal indicative of the blood glucose level in the blood being tested, which is then supplied to contact areas located near the rear or contact end of the sensor. For optically read or photometric sensors, a reflectance reading can determine the color change indicative of the glucose concentration in the blood/reagent mixture.
As with all medical diagnostic devices, contamination is of major concern. It is necessary to avoid contamination of both equipment and personnel by fluids, and to avoid contamination of a patient with fluids from others. For photometric blood glucose monitors in particular, a major concern is contamination of the read-head by blood. Blood on the optical read-head can give rise to erroneous measurements. To address this problem, current sensors have been designed so that they are inoculated with a patient's blood before the sensor is placed in the meter. While this configuration reduces the risk of contamination for the patient, the meter can still become contaminated with blood. In addition, this process is less convenient for the user.
To address the risk of meter contamination, some sensors have been designed to include a reactive membrane stretched across a through opening in a shaped sensor tip. While such sensors reduce the risk of meter contamination over conventional sensors, there still remains the risk that the read-head of the meter can become contaminated. The reactive membrane does not completely cover the through opening, allowing the possibility that blood may leak onto the meter or read-head either through the membrane or around the membrane/through opening juncture.
Manufacturing cost is another concern that exists with sensors that include a reactive membrane stretched across a through opening. Due to the large number of sensors a diabetic may use, even a minor reduction in the manufacturing cost of a sensor can result in substantial savings to the diabetic end user. Applying a separate membrane to a through opening involves extra manufacturing steps of handling a separate membrane and applying the membrane to the sensor base.
In addition to cost, reducing the sample volume is another concern that exists for current sensors. Current sensors require sample volumes anywhere from approximately 0.3 μL to 10.0 μL of blood. For example, in conventional capillary fill sensors, it is difficult to get a reasonable separation between the sample application point on the sensor and the read-head. To illustrate this, if the sensor protrudes 0.3 inches from the meter and the read-head is located 0.2 inches inside the meter case, then the capillary must be 0.5 inches long. Aside from resulting in a considerable waste of sample, this can also lead to a slow fill time and require larger punctures to extract the necessary quantity of blood.
Another challenge with current sensors is their packaging. Before use, the sensors need to be maintained at an appropriate humidity level so as to insure the integrity of the reagent materials in the sensor. Sensors can be packaged individually in tear-away packages so that they can be maintained at the proper humidity level. For instance, blister-type packaging methods have often been used. The packages can include desiccant material to maintain the proper humidity in the package. In order for a person to use an individual sensor for testing blood glucose, the package must be opened by tearing the seal. Alternatively, some packages require the user to exert force against one side of the package resulting in the sensor bursting or rupturing the foil on the opposite side. As can be appreciated, the opening of these packages can be difficult and may result in damage to the sensor. Moreover, once the package is opened the user needs to be sure that the sensor is not damaged or contaminated as it is being placed into the sensor holder and used to test the blood sample.
Other sensor packages, such as the one used in U.S. Pat. No. 5,630,986, issued May 20, 1997, and entitled Dispensing Instrument for Fluid Monitoring Sensors, also maintain a low humidity environment, but they are not easy to manufacture. One reason is that the symmetry of the circular packaging array does not match the rectangular symmetry of standard sheet sensor printing processes, necessitating handling individual sensors during packaging. The meter is also mechanically complex because of the mechanism required to extract the sensor from the blister pack. In addition, the number of sensors is not visible at a glance.
For the foregoing reasons, there is a need for a blood glucose sensor that reduces the risk of contamination, the manufacturing cost, and the sample volume. Further, there is a need for a package for such a blood glucose sensor that maintains the sensors at the proper humidity, is simple to use, and has a visual display of the remaining sensors.